Creep-fatigue interaction behaviour of a dispersion strengthened copper alloy was investigated at 22 and 250 deg.C. To determine the effect of irradiation a number of fatigue specimens were irradiated at 250 deg.C to a dose level of 0.3 dpa and weretested at 250 deg.C. The creep-fatigue interaction was simulated by applying a certain holdtime on both tension and compression sides of the cyclic loading with a frequency of 0.5 Hz. Holdtimes of 0,2, 5, 10, 100, and 1000 seconds were used. For a givenholdtime, the real lifetime and a number of cycles to failure were determined at different strain amplitudes. Post-deformation microstructures and fracture surfaces were investigated using transmission and scanning electron microscopes, respectively. Themain results of the investigations are presented and their implications are briefly discussed in the present report. The central conclusion emerging from the present work is that a holdtime of 10 seconds or less causes a drastic decrease in the reallifetime as well as in the number of cycles to failure, particularly at low levels of strain amplitudes. A combination of higher temperature, higher strain amplitude and longer holdtime, on the other hand, may lead to an improvement in the lifetime. Theirradiation at 250 deg.C to a dose level of 0.3 dpa does not play any significant role in determining the lifetime under creep-fatigue testing conditions.